Abstract A23: Alternative cyclin D1 transcripts in Mantle Cell Lymphoma
Authors: Naazneen Khan, Chioniso P Masamha
Journal: Blood Cancer Discovery (2022)

Abstract Mantle Cell Lymphoma (MCL) is a rare aggressive subtype of Non-Hodgkin’s Lymphoma. Upon diagnosis, treatments are varied and there is no universal standard of care. MCL is considered clinically incurable upon relapse. Better understanding of the development of MCL at the molecular level is needed. The initiating event is a hallmark (11; 14) translocation event that juxtaposes cyclin D1 (CCND1) downstream of the IgH enhancer element thus activating protein expression. This IgH recombination precedes the MCL diagnosis by several years. By itself, expression of cyclin D1 is insufficient for tumorigenesis. However, increased cyclin D1 expression combined with alterations in one of several DNA repair genes facilitates lymphomagenesis characterized by high genomic instability. Interestingly at the mRNA level, CCND1 transcripts containing the full length 3`untranslated regions (3`UTRs) have a half-life of ~30 minutes. CCND1 transcripts containing truncated 3`UTRs have a longer half-life up to ~8 hours resulting in increased translation. A subset of MCL patients with highly proliferative disease express CCND1 mRNAs with truncated 3`UTRs. Wiestner et al showed that truncated CCND1 3`UTR expression was associated with a reduction in patient survival by almost two years. While CCND1 3`UTR shortening in 20% of patient samples was due to mutations, the mechanisms driving this event in the rest of patients remain unknown. Our goal is to identify the different truncated CCND1 transcripts in MCL and determine how they are expressed. Using 3′Rapid Amplification of cDNA ends (3′RACE) we previously identified a novel fusion transcript where a short CCND1 3′UTR sequence was linked to intronic sequences of the MRCKB/CDC42BPB gene. In order to measure levels of expression of differently sized CCND1 3`UTR transcripts we used specifically designed primers for qRT-PCR. To determine the type of truncated CCND1 3`UTR expressed in other MCL cell lines we used 3′RACE. Iso Sequencing was used to verify the occurrence of the novel CCND1/MRCK fusion transcript. Cell viability assays were used to determine the impact of targeting the CCND1/MRCK fusion or cyclin D1 activated cyclin dependent kinase 4/6 inhibitor. Our qRT-PCR results showed that most of the MCL cell lines predominantly expressed CCND1 transcripts with truncated 3′UTRs with the exception of Mino-1 where the longer 3′UTR was more dominant. The 3′RACE results indicate that different mechanisms may result in the expression of the truncated CCND1 3`UTR transcript in each cell line. Iso Sequencing data identified 1,032 total reads supporting the CCND1/MRCK fusion transcript verifying our 3’RACE results. Our results suggest that there are different molecular mechanisms being used to regulate cyclin D1 expression in MCL. Cell viability assays showed decreased cell proliferation. In conclusion, identifying and understanding the mechanisms of expression of different CCND1 transcripts has potential in understanding MCL pathogenesis and the development of MCL therapeutics. Funding: 1R01-GM135361-01 to C. P. Masamha. Citation Format: Naazneen Khan, Chioniso P Masamha. Alternative cyclin D1 transcripts in Mantle Cell Lymphoma [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A23.